What are the safety concerns associated with wheatgrass?

Website info says. Wheatgrass is generally considered safe, although a few individuals have reported nausea, headaches, hives, or swelling in the throat within minutes of drinking its juice. Hives and swollen throat are often signs of a serious allergic reaction and should be handled as an emergency. Anyone having these kinds of symptoms after ingesting wheatgrass may have even more severe reactions to it later.